1. Field of the Invention
The present invention relates to new oxabicycloalkanes and to processes for their preparation. The compounds are useful materials in the preparation of insecticidally active synthetic pyrethroids.
2. Description of the Prior Art
The general formula of one class of pyrethroids described in U.S. Pat. No. 4,024,163 may be represented as follows: ##STR1## where each asterisk denotes an asymmetric carbon atom; each X is a halogen atom and R is a member of a group of radicals known to impart insecticidal activity to the molecule, e.g. 3-phenoxybenzyl or alpha-cyano-3-phenoxybenzyl. As these pyrethroids combine exceptionally good insecticidal properties with a very low mammalian toxicity, they are of great interest to the agrochemical industry and considerable effort has been expended in finding economic routes for their production.
It is known that the stereoisomeric form of the acid portion of the ester of formula A should be in the (1R, cis) form for maximum insecticidal activity, i.e. the absolute configuration at carbon atom 1 is R and the two hydrogen atoms on carbon atoms 1 and 3 are in a cis relationship. This nomenclature is known as the Elliott nomenclature and is defined in M. Elliott, A. W. Farnham, N. F. James, P. H. Needham and D. A. Pullman, Nature, 248, 710 (1974).
It follows, therefore, that if these stereoisomeric esters of formula A are to be prepared, either a stereo-specific chemical route is required or the desired stereoisomer must be obtained from a racemic form by physical separation techniques. The latter are expensive and laborious and not readily employed on an industrial scale. In a stereo-specific route the naturally-occurring substance (+)-3-carene is used, whose formula is as follows: ##STR2## This compound is an inexpensive, readily available, natural terpene and in the present application are disclosed processes in a stereo-specific route from (+)-3-carene to pyrethroid esters of formula A.